Optical coherence tomography (OCT) has been viewed as an “optical analogy” of ultrasound sonogram (US) imaging since its invention in early 1990's. Compared to the conventional image-guided interventions (IGI) using modalities such as magnetic resonance imaging (MRI), X-ray computed tomography (CT) and ultrasound (US), OCT has much higher spatial resolution and therefore possesses great potential for applications in a wide range of microsurgeries, such as vitreo-retinal surgery, neurological surgery, otolaryngologic surgery and cochlear implantation. It has recently been demonstrated that OCT can be highly effective in freehand or robotically assisted retinal imaging or cochlear implantation, for example. A single-mode fiber can be lensed with state-of-the-art micro-optics to form a light beam with a spot size around 11 μm to 18 μm in retinal imaging, gastrointestinal endoscopy, coronary artery imaging, and needle-based Doppler OCT. Thus, OCT fiber optic sensing and imaging are becoming powerful tools for non-destructive cross-sectional imaging of biological tissues.
Retinal surgery is one example of microsurgery. In current practice, retinal surgery is performed under an operating microscope with free-hand instrumentation. Human limitations include an inability to clearly view surgical targets, physiological hand tremor, and lack of tactile feedback in tool-to-tissue interactions. In addition, tool limitations, such as lack of proximity sensing or smart functions, are important factors that contribute to surgical risk and reduce the likelihood of achieving surgical goals. Current instruments do not provide physiological or even basic interpretive information. Surgical outcomes (both success and failure) are limited, in part, by technical hurdles that cannot be overcome by conventional instrumentation.
An injector is a device that may be used by a surgeon, for example, to deliver small volumes of drug, solutions, or other materials into biological tissues or cells. Examples of injection include delivering of various drugs to biological tissues including, but not limited to, those as delicate and fragile as retina or as robust as heart muscle. In many circumstances, it is more convenient to use a simple hand-held injector for injection and/or a manually-scanned probe for obtaining OCT images of tissues and organs which might otherwise be inaccessible using standard mechanical scanning heads. A hand-held instrument has the following advantages. First, it is small and lightweight, making it easy to access tight spaces. Second, surgeons are intimately familiar with hand-held instruments which can leverage the surgeons' experience and skills with little training. Third, a small hand-held instrument offers greater safety because the surgeon can more easily override or remove the instrument in cases of malfunction.
A hand-held instrument, however, poses additional challenges over mechanically-rigid instruments. For example, the drug may need to be accurately delivered to a specific site or layer. Researchers have employed a phase-contrast inverted microscope to guide a capillary injection system and determine the cells injected based on timing. However, challenges remain for accurate injection. First, the surgeon must insert and maintain the tip of the injector at the targeted location with an accuracy that is on the order of tens of micrometers. Second, hand tremor, or physiological motion (e.g. the breathing and/or heartbeat, as well as volitional movement of the surgeon and/or patient) can damage surrounding delicate tissues or cause localized hemorrhage or other injury and pose a high risk to the safety of the patient during injection. The resulting involuntary changes in distance between the injector and surgical tissue surface, although usually on the order of a few hundreds of micrometer at less than 5 Hz, may cause serious error due to the scale of microsurgery. The “injector-tissue” relative motion is especially critical in the case of surface operations such as retina vitreous surgery and cerebral cortex neurosurgery where the fragile tissue's axial involuntary motion is a primary concern that requires high dexterity and constant attention from experienced surgeons.
Currently, no hand held injection system can satisfy all of the above challenges during injection. There remains a need for improved injector systems and methods for microsurgical applications.